The present invention relates to a method of manufacturing semiconductor integrated circuit devices, and, more particularly, to an effective technique applicable to a type of lithography which uses a phase shift mask during exposure processing.
For example, in Japanese Laid-open Patent Publication 83032/1994, in describing a mask having a structure which uses a resist for writing electron beams or a silicon oxide film as a material of a phase shifter of a phase shift mask, the attenuation of the exposure light derived from the light transmittance of a shifter portion in the form of a film is mentioned as a problem. Then, as means for solving this problem, the publication discloses a technique to reduce the attenuation of the exposure light at the shifter portion by exposing identical mask patterns of two respective physically separate masks by superposition exposure.
Further, Japanese Laid-open Patent Publication 233429/1999 discloses an exposure technique in which multiple exposures are produced by changing the exposure conditions in accordance with the characteristics of patterns which constitute objects to be exposed.
Further, Japanese Laid-open Patent Publication 111601/1999 discloses a super resolution double scanning exposure technique to solve a problem which occurs when two masks are used in multiple exposure processing, wherein the mask exchanging operation becomes necessary at the time of the exposure processing so that the throughput of the exposure step is lowered and the manufacturing cost is increased, in addition to other problems. In this technique, identical mask patterns are formed on different planar positions of one sheet of a mask and then multiple exposures are performed over the mask patterns by a scanning system exposure processing.
Further, Japanese Laid-open Patent Publication 197126/1993 discloses an exposure technique which arranges shifter patterns which cross each other at different planar positions over the same mask substrate, and then performs a multiple exposure by shifting the shifting patterns which cross each other by a half pitch and transfers a pattern to the crossing region.
Further, Japanese Laid-open Patent Publication 12543/1998 discloses a superposition exposure technique which performs a multiple exposure by shifting patterns which cross each other by a half pitch and transfers a pattern to the crossing region.
Still further, Japanese Laid-open Patent Publication 143085/1999 discloses a multiple exposure technique which performs a multiple exposure by using two-luminous flux and ordinary light and transfers a pattern to the crossing region.
Heretofore, in the manufacture of semiconductor integrated circuit devices, the lithography technique has been used as a method for transferring fine patterns onto a semiconductor wafer. In the lithography technique, a projection exposure apparatus is mainly used and an integrated circuit pattern is formed by transferring a pattern of a photo mask mounted on the projection exposure apparatus onto the semiconductor wafer.
As such projection exposure apparatuses, there exist a stepper which transfers the pattern of the photo mask by a step-and-repeat process and a scanner which scans the photo mask and the semiconductor wafer in opposite directions from each other and continuously transfers slit-like exposure areas. The largest difference between the stepper and the scanner lies in the fact that the stepper transfers the pattern by using the entire surface of a projection lens, while the scanner transfers the pattern by using only a slit-like portion extending in a diameter direction of a projection lens.
By the way, the refinement of patterns constituting the semiconductor integrated circuit devices is achieved by the enhancement of the performance of a reduced size projection exposure apparatus which is mainly used in a lithography step of a process of manufacture of semiconductor integrated circuit devices. However, to further enhance the fine processing of the patterns, it becomes necessary to enlarge the diameter of the numerical aperture NA of the reduced size projection exposure apparatus. Particularly, to obtain a high resolution in the fine hole patterns arranged with high density, it becomes necessary to set the exposure light to have a shorter wavelength and higher NA. However, this requires a huge amount of facility investment, and, hence, it is not realistic to undertake a new facility investment without completing the depreciation of the semiconductor manufacturing device under the current situation in which the fine processing level of the semiconductor integrated circuit devices has been accelerated year by year. Accordingly, recently, in the lithography technique, a photo mask which includes phase information on lights passing through the photo mask, such as a phase shift mask, has been under development. The phase shift mask technique is a technique which enhances the resolution and the focal depth by operating on the phase of light which passes through the photo mask (including a reticle). As such a phase shift mask technique, for example, there exists the Levenson type phase shift mask technique which arranges a phase shifter on one of neighboring light transmission regions to make the phases of the lights which pass through both light transmission regions inverted relative to each other and the like.
A groove shifter is a phase shifter which forms recessed portions in a transparent film or a transparent mask substrate or the like, which constitutes a lower layer than a light shielding film over the mask. For example, the phase shifter is formed by digging grooves in the transparent film or the transparent mask substrate exposed from one of neighboring light transmission patterns of the mask such that the phases of lights which pass through the neighboring light transmission patterns are inverted by 180 degrees relative to each other.
The inventors, however, have found that the phase shift mask technique having the above-mentioned groove shifter structure has the following problems.
That is, a first problem is that, along with the refinement of the patterns, the control of the phase difference is required to satisfy a high accuracy. For example, in case KrF excimer laser light is used as the exposure light, the depth of the groove shifter is approximately 245 nm. Assuming that the allowable phase error is 2 degrees, the groove forming amount of the mask substrate is required to satisfy an accuracy of approximately ±3 nm. However, the mask substrate is constituted by a glass substrate which is made of quartz or the like, and it is impossible to perform the depth adjustment or the like by temperature control or the like. Accordingly, it is difficult to form grooves which fall within such a range (accuracy) by using dry etching processing for forming the groove. In this manner, with respect to the phase shift mask having a groove shifter structure, the absolute value control of the phase becomes a large problem.
A second problem is that, in the phase shift mask, due to the mask structure provided for producing the phase difference, the dimensional accuracy of the transfer patterns is lowered. For example, in the groove shifter structure, due to the influence of the side surfaces of groove-formed portions of the mask, the amount of transmitted light is decreased and eventually a difference arises between the dimensions of respective patterns which are transferred by the light passing through a place in which the groove shifter is arranged and the light passing through another place in which the groove shifter is not arranged and which is disposed close to the previous place. To cope with this, in the groove shifter portion, a structure (fine eaves type groove shifter structure) which makes the transparent film or the transparent mask substrate overhang in the groove width direction, so as to have end portions of the light shielding patterns protrude like eaves, is adopted. However, along with the refinement of the transfer patterns, there exists the problem that the dimensional difference between the transfer patterns cannot be eliminated even with the fine eaves type groove shifter structure.
A third problem is that the manufacturing of masks becomes difficult due to the highly accurate absolute value control of phases and the formation of a fine eaves type groove shifter. Further, along with the refinement of the transfer patterns, the mask defect inspection and the mask correction are required to satisfy a high accuracy. Accordingly, the yield rate is decreased.
Accordingly, it is an object of the present invention to provide a technique which can attenuate the absolute value control accuracy of the phase in a mask having a groove shifter structure.
It is another object of the present invention to provide a technique which can enhance the dimensional accuracy of transfer patterns by using a mask having a groove shifter structure.
It is a still another object of the present invention to provide a technique which can attenuate the detected dimensions of the inspection of a mask having a groove shifter structure.
It is a further object of the present invention to provide a technique which can enhance the ease of manufacture of masks having a groove shifter structure.
It is a still further object of the present invention to provide a technique which can enhance the yield in the manufacture of masks having a groove shifter structure.
The above-mentioned objects, other objects and novel features of the present invention will become apparent in view of the description of the specification and the attached drawings.